Abstract ================== NOTICE: THIS ABSTRACT WAS EXTRACTED FROM APPLICATION AND HAS NOT BEEN PROOFED BY AN SRA.WHEN THERE ARE PROBLEMS WITH THE APPLICATION SCANNING PROCESS, THE EXTRACTED TEXT MAY BE INCORRECT OR INCOMPLETE. ================== Francisella tularensis, the etiological agent of tularemia, is a Gram-negative intracellular coccobacillus that is adept at inducing acute, fatal disease in a number of mammalian species, including humans. F. tularensis is well-recognized as one of the most dangerous bacterial pathogens known because of its low infectious dose (<10 organisms), ease of aerosolization, multiple routes of infection, and capacity for inducing severe morbidity and mortality. Little is known about the molecules that F. tularensis uses to invade host cells and subsequently cause disease, but outer membrane proteins (OMPs) are likely instrumental in this process. Indeed, OMPs have been shown to be virulence factors in many other bacterial pathogens and, for this reason, are ideal vaccine targets. During my postdoctoral research, I developed a method to extract and purify F. tularensis OMPs, which has led to the identification of nearly 30 new OMPs. In subsequent studies, I demonstrated that an OMP-based vaccine protected mice against virulent Type A F. tularensis pulmonary challenge. While these results are compelling and have greatly advanced the tularemia research field, the bacteria used for these studies were grown under rich media conditions. To date, little has been reported about OMP expression during host infection, yet it is reasonable to hypothesize that F. tularensis dramatically alters its OMP profile in vivo to facilitate host cell invasion and disease. As such, this research proposal will extend my previous findings by: (1) Using rRT-PCR to examine whether known OMPs are up- or down-regulated in the mammalian host;(2) Discovering new OMPs that are exclusively expressed in macrophages;(3) Identifying new virulence factors through the generation of OMP-deficient mutants and assessing the infectivity of these mutants in a mouse pulmonary infection model;and (4) Characterizing both the antibody-mediated and cell- mediated immune responses against OMPs that confer protection against F. tularensis pulmonary challenge. These project subaims are designed to answer fundamental questions about F. tularensis virulence as well as the correlates of protective immunity. Additionally, this proposal has practical applications for the development of safe, efficacious vaccines to prevent F. tularensis infection and disease. Francisella tularensis is important not only because of its classification as a Category A Select Agent, but because of its rapid intracellular pathogenesis. Little is known about the surface molecules of F. tularensis, yet such information could provide vital information for the development of a safe, efficacious vaccine against tularemia. The projects outlined in this proposal seek to identify bacterial molecules involved in infection and characterize protective immune responses.